Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

502
FXUS63 KLOT 040605
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
105 AM CDT Sat Jul 4 2026

.KEY MESSAGES...

- Additional rounds of showers and storms are expected at times
  through the weekend. A few storms could be strong to severe
  this afternoon, mainly south of Interstate 88.

&&

.DISCUSSION...
Issued at 243 PM CDT Fri Jul 3 2026

Rest of Today/Tonight:

Round one of thunderstorms is surely living up to expectations
with numerous measured severe wind gusts ranging from 60 to 73
mph. While the main push of storms is now moving toward Lower
Michigan, a few more cellular storms continue to percolate along
the remnant outflow boundary stretching southwestward from
Joliet to Lacon to Macomb, Illinois. North of the outflow
boundary, it feels the most comfortable it has in the past week
with temperatures largely in the low to mid 70s. Meanwhile,
south of the front, it`s hot and sticky with heat index values
in the 100 to 105F range.

Focus is on the potential for a second round of storms this
evening. While southwesterly flow on the southern side of the
outflow boundary is not particularly strong (10 to locally 15
kt), have been noting the beginning of the northward retreat of
the unstable airmass back toward northwestern Illinois. Just how
far northwest the unstable airmass retreats is an item of low
confidence, but suspect it will be able to reach I-80 and
perhaps even I-88 by this evening ahead of an upper-level
shortwave currently moving through the southern Iowa region. As
a result, concern remains for another round of storms near the
frontal boundary (perhaps extending eastward from ongoing storms
near Kansas City, MO) as the wave moves approaches our area.
Timing the second round still looks to start sometime in the 6
to 7 PM timeframe with scattered storms continuing through the
overnight hours.

While the wave of storms that came through earlier today were
anchored by a notable 500mb wind max, flow this evening will be
weaker and more on the order of 25-30 kt. As a result, current
thinking is that coverage of severe weather this evening will
not be as high as it was with the first round of storms.
Nevertheless, moisture-laden MUCAPE >3000 J/kg will still
support water-loaded microbursts with a threat for torrential
downpours and localized wind damage. In addition, with storms
more likely to adopt a west-to-east orientation this evening, do
have concern for localized flash flooding particularly if the
front does make it back toward the I-88 corridor where 3 to
locally 5 inches of rain fell last night. If it becomes clear
such a threat will materialize, will consider hoisting a short-
fused Flash Flood Watch.

Tomorrow / Independence Day:

At least isolated showers and storms may be ongoing at daybreak,
though most guidance suggests coverage should wane by mid-
morning. Global guidance than advertises another upper-level
shortwave or two pinwheeling into the area during the afternoon
hours, which will support additional rounds of thunderstorms. At
this point, confidence in where the frontal boundary (which
will mark the unstable airmass) will be by tomorrow afternoon
is quite low and depends on coverage of storms tonight. So,
unfortunately, cannot offer more than mid-range chance PoPs
areawide tomorrow in favor of further refinement as things
hopefully become more clear tonight. The same goes for Sunday.

Borchardt


Beyond the weekend the upper ridge begins to build back north
slightly with the embedded waves moving to our north. Meanwhile
another wave (or waves) will move within the ridge to our south
(and potentially stall out). Overall this favors shower/storm
coverage focusing mainly north or south of the area into mid-
week. Shower and storm chances return later in the week as the
ridge begins to break down again.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 105 AM CDT Sat Jul 4 2026

Key aviation messages:

- A period of SHRA/TSRA possible in the AM, mainly toward RFD
  (30% chance)

- Greater coverage of storms favored during the afternoon at all
  sites (18-01Z timeframe moving from west to east).

- Low confidence in wind direction trends through the afternoon

- Potential for fog/low stratus off the lake late tonight into
  early Sunday AM

Storms continue to weaken and shift southeast of the terminals
with lingering rain ending over the next 30-60 minutes.
Attention turns to convection currently over central Iowa that
will be moving east toward the area overnight through daybreak.
Confidence in convective trends remains low yet again with the
majority of guidance weakening these storms with eastward
extent. While it will be encountering a less favorable
environment, do have concerns that it will at least hold
together into part of NW IL. Have accordingly introduced
PROB30s for TSRA at RFD from 13-15Z to account for this.
Confidence remains too low for a formal introduction at the
Chicago terminals of an earlier round of storms.

A remnant MCV feature expected to drift east northeast toward
the region associated with a separate area of convection over
eastern Nebraska may serve as the focus for renewed TSRA
development across the area this afternoon. Have converted the
inherited PROB30 groups to TEMPOs with this update. The strength
of the storms remains lower confidence owing to a lake breeze
expected to push inland early in the afternoon which may help
focus the threat for severe weather mainly south of the
terminals.

Wind directions are expected to remain highly variable through
midday before a lake breeze moves inland in the afternoon
turning winds more solidly northeast. Any convection that
develops will also lead to varied wind directions at times
during the afternoon into early evening before settling back
into a northeast direction through early Sunday morning.

Lastly there is a signal for fog (potentially dense) and/or low
stratus (LIFR/VLIFR) over Lake Michigan that may try to ooze
inland late this evening through early Sunday morning.
Confidence is too low to include with this update but will be
monitored closely given it may have some dependence in how
convective trends also evolve later today.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch until 4 AM CDT early this morning for ILZ006-
     ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ103-ILZ104-
     ILZ105-ILZ106-ILZ107-ILZ108.

IN...Flood Watch until 4 AM CDT early this morning for INZ001.

LM...None.

&&

$$

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